Injectors of internal combustion engines have production tolerances after their manufacture. As a consequence, each injector outputs a different fuel quantity upon an actuation with the same signal. It goes without saying that an attempt is made to keep said deviations as small as possible.
The injectors which are addressed here are those, in which the movement of the needle of the injector is controlled by way of an actuator directly, that is to say without a servovalve, in particular via direct contact, via levers, or via a hydraulic coupling. Directly controlled injectors of this type have no operating leakage. Therefore, the fuel quantity which is removed from the pressure accumulator during one cycle corresponds (considered dynamically) to the injection quantity which an injector has introduced into the combustion chamber of the internal combustion engine.
In injectors of this type with a directly coupled nozzle needle, the deviations in the injection quantity which are mentioned in the above text can be standardized as follows:
Type 1: deviation in opening and closing times
Type 2: deviation in the maximum rate
Deviations which consist of a combination of the two types specified above are likewise possible.
Various methods and strategies are known, in order to reduce or eliminate deviations of this type. In a first known method, classification of the corresponding injectors takes place. Here, the injectors are measured at certain points, and the corresponding deviations are encoded. Subsequently, the encoding is transmitted to the control device of the internal combustion engine, in order for it to be possible to apply corresponding adoption functions.
In another method, a closing time regulation is used to eliminate deviations of type 1. Here, the closing times of the injectors are detected and the deviations are corrected.
In yet another method, cylinder pressure indexing is carried out for combustion process checking and cylinder balancing. In another method, cylinder balancing and quantity estimation take place on the basis of a crankshaft acceleration signal.
The abovementioned methods are as a rule complicated and capable of improvement in relation to the accuracy of the obtained results.